Rather than fuses, what about using JBL SK3 Crossover Protection Bulbs instead.
If you had already ordered a few of the SK3 bulbs, I donít think they come with instructions on how to use them in your own special application. But, donít fret about it too much because JBL is using them in a lot of different crossover networks. So, I suspect that one of the following will turn up a schematic that you can copy.
JBL MR Series, JBL MR800 Series, JBL MR900 Series, JBL SF Series, JBL Cab Series, JBL TR Series, JBL Sound Factor Series, JBL Control Series, JBL MP Series, JBL M-Pro Series, JBL Eon Non-Powered Series, JRX Series.
The SK3 bulb does more that than act as a just a fuse. Because the tungsten filamentís resistance varies so greatly with temperature, it can act more like a compressor preventing damage to the driver without blowing like a regular fuse. In the TR125 example below, the two SK3 bulbs and the 16 ohm resistor form a series attenuator for the HF driver. At low power levels the bulb resistance is low and there is no compressor effect. But at excessively high power levels the bulbs light up and their resistance increases, which will reduce the power going to the HF driver. And at catastrophic overload power levels the bulbs will burn out, leaving only the 16 ohm resistor to supply a very limited amount of power to the HF driver until the SK3 bulbs can be replaced. I suspect that in other networks, R1 value maybe different depending on the HF driverís impedance and power handling characteristics.
The JBL/UREI - 525 active crossover manual has some frequency/capacitance tables
I am not suggesting that you replace your existing passive crossover networks. Just modify them to include SK3 bulbs if you are so concerned about protecting your drivers. Now if I understand your system correctly. You have a XR1001 electronic network between the woofers and the midrange horns. The BGW750C amp feeds the woofers and the BGW250D feeds both the midrange and the 2404s. And the 6000Hz passive network slits the signal between the midrange and 2404s. In the schematic below, what I donít know is, what are the correct R1 and R2 values for your application. But, this is something that can be derived from studying other JBL networks that have SK3 bulbs. Now, if the 2404H driver has the same power handing as a 2412H driver, then the appropriate R1 value would be a 16 ohm 10 watt resistor. Otherwise, then a different value would be needed. Actually, for a home audio system I donít see the need to fuses or SK3 protection bulbs. But, in a pro sound reinforcement system where microphone feedback could route several hundred watts into a HF driver the SK3 bulbs seem like a really good idea.
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